1. Field of the Invention
This invention relates to a mechanism for deflecting a surgical instrument inserted into an endoscope, and/or a distal end of the endoscope shaft, and to a method of causing the distal end of the surgical instrument and/or endoscope shaft to bend during a surgical procedure. The invention also relates to a self-steering laser fiber.
Although not necessarily limited to a particular surgical application, the invention is especially suitable for use in deflecting the end of a urological endoscope such as a ureteroscope, nephroscope, or cystoscope, in order to direct a surgical laser at a kidney stone for the purpose of fragmenting the stone.
According to a first preferred embodiment of the invention, a mechanism is provided for deflecting a laser-delivery glass optical fiber inserted into the working channel of the endoscope to reduce strain on a conventional tensioned-wire shaft deflection mechanism, and for keeping the end of the glass fiber in the field-of-view of an optical fiber bundle embedded in the endoscope. In this embodiment, the deflecting mechanism is a sleeve which surrounds an end of the laser-delivery fiber and which includes a shape memory alloy having a transformation temperature slightly higher than body temperature. When an appropriate fluid such as water having a temperature corresponding to the transformation temperature of the shape memory alloy is supplied to the working channel, the sleeve assumes a predetermined bent shape to deflect the end of the fiber.
According to a second preferred embodiment of the invention, the deflecting mechanism is a sleeve embedded in the shaft of the endoscope, the sleeve again including a shape memory alloy having a transformation temperature slightly higher than body temperature so as to bend and thereby deflect the end of the shaft when a fluid having a temperature greater than or equal to the transformation temperature is supplied to the working channel. The deflecting mechanism of this embodiment may supplement or replace the conventional tensioned-wire deflecting mechanism.
2. Description of Related Art
Over the past 25 years, the field of medical endoscopy has substantially matured. Today, surgeons can not only use endoscopes to view inside of hollow organs, such as the urethra and rectum, without the need to make incisions, but they can also extract tissue samples for subsequent biopsy or use the endoscope to guide an optical fiber that can deliver intense laser radiation to accomplish surgical functions such as cutting or cauterizing tissue or fragmenting kidney stones.
Modern endoscopes used for urological applications (ureterscopes) are highly engineered instruments made by a number of suppliers including Olympus, Wolf, Stortz, and ACMI. They are relatively expensive, with purchase prices ranging from $10,000 to $15,000. Further, they are inherently delicate due to a number of stringent functional requirements that must be accommodated within a small shaft diameter (typically less then 3 mm) that is limited in size by human anatomy.
The functional requirements include (1) substantial flexibility to conform to the contours of the natural pathways in a body, (2) the ability to convey illumination from an external light source to the distal end of the endoscope (inside a body), (3) the ability to convey high quality images from inside the body to the surgeon, (4) inclusion of a hollow working channel to insert small instruments such as biopsy scissors or an optical fiber to perform laser surgery functions, and (5) means for steering the distal end of the shaft to increase the field of view.
A cross section of the shaft 1 of a modern endoscope (ureterscope) is shown in FIG. 1. The shaft 1 is made up of an outer plastic jacket 2 and a plastic extrusion 3. Plastic extrusion 3 encloses bundles 4 of very small diameter optical fibers 5 for illuminating and viewing tissues in viva, and a metal tension wire 6 situated within a clearance hole 7 for bending or curving the end of the shaft. In addition, extrusion 3 defines a working channel 8 through which surgical instruments such as biopsy scissors and laser-delivery glass optical fibers may be inserted.
FIGS. 2a and 2b show side views of the shaft 1 before and after tension is applied to the metal tension wire 6. The fiber bundles and working channel have been omitted from FIGS. 2a and 2b for purposes of illustration. The tension wire is free to move inside of clearance hole 7 along the entire length of the shaft, which in the case of a ureterscope is typically about two feet. A plurality of open wedge segments 11 are cut into the plastic extrusion 3, and the end of the wire is firmly secured to the distal tip of the endoscope, for example by molding a hook shaped end 9 of the tension wire into the plastic wall 10 of the tip. When tension is applied to wire 6 by pulling on the proximal end of the wire so that it moves within clearance 7 in the direction of arrow A relative to the endoscope, the wire pulls on the distal end of shaft 1 to which it is fixed, causing the distal end to bend in the direction permitted by the open wedge segments 11 by an angle of up to 180°. Once bent, as shown in FIG. 2b, the endoscope may be rotated by the surgeon, as indicated by arrow B, to permit viewing in any direction.
While the functionality of such endoscopes is impressive, their ruggedness is marginal. Periodic repairs are routine costing from $3,000 to $6,000. One of the major causes for failure requiring repair is due to permanent distortions in the shape of the shaft cross section caused by the tension applied to the steering wire, as shown in FIGS. 3a and 3b. FIG. 3a shows the undistorted endoscope shaft and FIG. 3b shows the distorted shaft, with the distortion being indicated by reference numeral 14. Such a distortion limits the range of angles over which the distal end of the shaft may be steered or bent to less that the desired 180 degrees.
To make matters worse, if an object is inserted into the working channel that is inherently rigid, like the large-diameter glass optical fiber used to guide laser beams for surgical functions, greater tensile forces must be applied to the steering wire to overcome the extra rigidity. This typically results in a reduction in the periodic repair interval for the endoscope that is undesirable both due to high cost and a temporary loss of use of the endoscope.
The present invention offers a means to reduce or overcome the inherent rigidity of large diameter laser-delivery optical fibers used or other instruments used in endoscopes and thereby increase the useful service period between repairs, by providing a deflection mechanism for the instrument that is separate from the endoscope shaft deflection mechanism. The invention may also be used as a supplemental means to steer the endoscope shaft, i.e., to assist the tension wire in steering, and therefore further reduce the tensile force in the steering wire and extend the periodic repair interval of endoscopes.
In addition to reducing strain on the endoscope deflection mechanism and associated distortion of the endoscope shaft, by overcoming the inherent rigidity of instruments inserted into the working channel of the endoscope and/or by providing a supplemental means of deflecting the shaft, the invention helps resolve another problem, illustrated in FIG. 4, that is experienced by surgeons who use endoscopes to perform surgery by delivering a powerful laser beam through an optical fiber inserted into the working channel. The problem is that the tip 13 of the laser-delivery fiber 12, which extends out of the working channel 8 during laser delivery, may not always be in the field of view a of the lens 14 that is conventionally provided at the end of optical fiber bundle 4 to facilitate viewing of the fiber tip 13. A surgeon must be able to view the tip 13 of the surgical fiber 12 to ensure that it is properly positioned before launching a high power laser beam into the fiber to accomplish a surgical function.
Because of the offset Y between the coherent fiber bundle 4 and the working channel 8, laser delivery fiber tip 13 must protrude some distance beyond the end 10 of shaft 1 (typically several millimeters, and up to about 5 mm). However, as shown in FIG. 4, the fiber 12 may still be unfavorably positioned as a result of random orientation of the fiber within the constraints of the working channel, which causes tip 13 to point away from the field of view. In that situation, the fiber tip may be rotated into the field of view α, but only if the laser-delivery fiber has sufficient curvature, as indicated in dashed-line by reference numerals 12′ and 13′.